An investigation into poor retention first determines whether the errors were habitual or arose later. If ikhtilāṭ is established, critics gather the dates of individual pupils’ auditions and assess each route in its proper period.
They then search for independent transmissions. If the weakness is remediable and credible equal or stronger support exists, the collection of routes may justify a grade such as ḥasan li-ghayrihi. A weak narrator does not make every report demonstrably false, nor is every weak report necessarily capable of strengthening.
The resulting judgment must integrate integrity, precision, severity of the defect, chronology, independence of routes, and agreement in content. The next subject turns to the basic distinction between isnād and matn.